The present invention relates to a method of laying roofing felt on roofs, said roofing felt containing bitumen which is solid at ambient temperature and softens at an increased softening temperature, in which method length of roofing felt are brought to overlap each other in overlap zones of predetermined width, and welded together by heating the bitumen to said softening temperature by means of a heat-emitting member. The invention also relates to a means for use when laying roofing felt of the type described above, said means including a heat-emitting member.
When laying roofing felt it has been usual to spread molten tar on the surface and on the edge portion of an adjacent length and then roll out the roofing felt on the tar-coated surfaces to produce overlap joints. The tar is usually heated to liquid state in a container placed on the roof, using an open flame. Due to the considerable fire risk and the fact that many extensive fires have occurred, this method entailing an open flame will in future only be permitted under personal responsibility and at great risk.
It is also known to heat bitumen with the aid of pre-heated air or a gas flame, the air of the gas flame being directed into the overlap zone while the edge of one length of roofing felt is left and then pressed down against the other edge portion as the softening process proceeds. The use of a gas flame will shortly be prohibited for the same reason as stated above. Like the method using a gas flame, the method using pre-heated air is performed at relatively low speed and in an uncomfortable working position, which may lead to uneven results.
The object of the present invention is to provide an improved method of laying roofing felt and welding together the lengths to form continuous welded seams considerably faster than said hot-air method and in a more ergonomically favorable manner.
The method according to the invention is substantially characterized in that, when the overlapping lengths are in contact with each other, an electric current is caused to pass through an electrically conduction heat-emitting member arranged within and extending continuously along the entire overlap zone, in that the heat-emitting member is supplied with energy by induction by means of an induction apparatus that emits a variable magnetic field inducing current of suitable strength in the heat-emitting member to generate heat in the heat-emitting member, said heat being emitted to at least one of the opposing portions of the lengths within the overlap zone so that the bitumen in at least said portion is brought to its softening temperature and the lengths are welded together at said opposing portions to form a tight, continuous overlap joint.
The means according to the invention is substantially characterized in that the heat-emitting member is electrically conducting so that an electric current is caused to pass through it when the overlapping lengths are in contact with each other, said heat-emitting member being arranged within and extending continuously along the entire overlap zone, said means also including at least one induction apparatus arranged to supply energy by means of induction to the heat-emitting member, said induction apparatus being arranged to emit a variable magnetic field inducing current of suitable strength in the heat-emitting member to generate heat in the heat-emitting member, said heat being emitted to at least one of the opposing portions of the lengths within the overlap zone so that the bitumen in at least said portion is brought to its softening temperature and the lengths are welded together at said opposing portions to form a tight, continuous overlap joint.